1. Field of the Invention
The present invention relates to form measuring instruments, and more particularly, to an improvement of a surface roughness measurement mechanism.
2. Prior Art
Form measuring instruments have been conventionally used to measure the shapes of workpieces precisely. Form measuring instruments include roundness measuring machines provided with a rotation mechanism, and form measuring instruments provided with a linear movement mechanism, such as surface roughness measuring machines, contour profiling measuring machines, and three dimensional coordinate measuring machines.
For example, a roundness measuring machine is used to measure the roundness of a cylindrical workpiece. A conventional roundness measuring machine includes a rotation mechanism such as a rotating table and a rotation-angle measurement device provided for the rotation mechanism. The rotation-angle measurement device obtains positional information of the cylindrical workpiece, required for roundness measurement. A general-purpose rotation-angle measurement device can be used as a conventional rotation-angle measurement device, such as those disclosed in Japanese Unexamined Patent Application Publication Nos. Hei-6-42942, 2000-136944, and 2004-245634.
In the roundness measuring machine, the cylindrical workpiece is placed on the rotating table; and while the rotating table is rotated, surface positions of the cylindrical workpiece are detected by a detector to obtain cross-sectional curve data of the cylindrical workpiece. Parameters used to measure roundness are calculated from the cross-sectional curve data obtained in this manner.
Precise measurement of a cylindrical workpiece includes surface roughness measurement in addition to roundness measurement.
Conventionally, a roundness measuring machine provided with a rotation mechanism is used for roundness measurement of a cylindrical workpiece; and a surface roughness measuring machine provided with a linear movement mechanism is used for surface roughness measurement of the cylindrical workpiece.
When separate form measuring instruments are prepared for roundness measurement and surface roughness measurement, however, a large space and a high expenditure are required.
Therefore, there has been a great demand for a single form measuring instrument that can be used for both roundness measurement and surface roughness measurement of a cylindrical workpiece. Especially for cylindrical workpieces, there has been a strong demand for the ability to use a roundness measuring machine to measure surface roughness.
When a roundness measuring machine is used for surface roughness measurement, satisfactory measurement may not be performed because the adoption of roundness measuring machines for this purpose has not yet reached a practical level: the reason for this is not fully known.
Therefore, a surface roughness measuring machine provided with a linear movement mechanism is conventionally used for surface roughness measurement of cylindrical workpieces, which can be rotated and measured with a rotation mechanism.
As described above, in this field, there is a strong demand for technology to be developed to perform more precise surface roughness measurement, but no appropriate conventional technology to make it happen has yet been obtained.